In an analysis of data from a large national database, patients who had radioiodine ablation had a small but statistically significant advantage in 10-year survival (90% versus 87.4%, P<0.0001), Paritosh Suman, MD, of the University of Chicago, and colleagues reported at the American Thyroid Association meeting here.

Papillary thyroid cancer has a good prognosis, and standard treatment involves surgical resection -- but clinicians can choose to add radioactive iodine for tumors believed to have a higher risk of recurrence. However, several studies have not confirmed a survival advantage with radioactive iodine.

Suman and colleagues looked at data from the National Cancer Database 1998-2012, totaling 108,565 patients with papillary thyroid cancer, followed for a mean of 7 years.

Radioiodine therapy was used in 47% of cases, with greater use in larger tumors: 29% for ≤10 mm tumors versus 58% for >40 mm tumors (P<0.001).

Suman and colleagues found that radioiodine ablation was associated with a small but significant overall survival benefit compared with no radioiodine therapy (90% versus 87.4%, P<0.0001).

There were advantages based on several characteristics, including tumor size. Those with the largest tumors appeared to glean the most benefit:

≤10 mm: HR 0.73, 95% CI 0.61 to 0.87, P<0.001

11-20 mm: HR 0.82, 95% CI 0.68 to 0.99, P=0.04

21-40 mm: HR 0.63, 95% CI 0.52 to 0.78, P<0.001

>40 mm: HR 0.62, 95% CI 0.47 to 0.81, P=0.001

"There was definitely a survival advantage in all groups, but this advantage was more pronounced in tumors larger than 4 cm," Suman said.

Patients of all ages also saw a survival benefit, but it was strongest for those 65 and older, and it was stronger for men than for women, Suman said.

And margin status saw a steep differentiation in benefit, as those with gross margins had the most significant survival advantage compared with negative, positive, and microscopic margin status.

In multivariate risk analyses, Suman and colleagues assessed patients by risk status, which took into account several factors including combined features including disease severity, demographic factors, and extent of operation:

Very low-risk: HR 0.74, 95% CI 0.67 to 0.81

Low-risk: HR 0.80, 95% CI 0.74 to 0.87

High-risk: HR 0.71, 95% CI 0.66 to 0.77

Suman noted that they did not analyze data on dose, disease-free survival, or sociodemographic factors because many of these data points were missing.

When asked by an audience member for his recommendations on microcarcinoma, Suman said that most of the time his institution gives radioactive iodine for multifocal cancer, but one of the limitations of their current dataset is that such information was not available.

"At this point, I do not think that for less than a 1-cm unifocal tumor we are going to change our practice based on a retrospective study," he said. "If we can, we will do a prospective randomized study to answer that question in a better way."

The difference between his team's study and others may be attributable to the fact that they are using a larger dataset, or it could have to do with the fact that practice has changed over the years and clinicians are now more selective about choosing appropriate candidates for radioiodine therapy, Suman said.

He pointed to an analysis of Surveillance, Epidemiology and End Results (SEER) data, also presented at the meeting, that similarly found a significant survival advantage from radioiodine therapy.

That study looked at 85,740 patients with differentiated thyroid cancer diagnosed between 1973 and 2009, among whom 43% had radioiodine therapy.

The treatment was associated with a 30% increase in overall survival (HR 1.3, P=0.002), according to Michael Bouvet, MD, of UC San Diego Moores Cancer Center.

That study did, however, find a negative effect of radioiodine therapy in patients with micropapillary carcinoma, and the researchers called for future studies to "investigate and confirm the negative effect seen in T1a patients."

Suman concluded that radioiodine ablation in papillary thyroid cancer is associated with a small but significant advantage in overall survival for most patients.

Hossein Gharib, MD, of the Mayo Clinic and president of ATA, noted in an earlier interview that researchers have also been looking at the use of radioiodine therapy at even earlier stages of disease -- in particular, for benign goiter.

"There have been a lot of data in the past 5 years that show radioiodine is effective in large goiters," Gharib said. "Radioiodine may be an alternative in patients who are high-risk for surgery, younger patients, and for those who don't want exposure to surgical treatment."

Gharib noted that European researchers have done a lot of work in this area and will be presenting their findings later in the meeting.

Suman disclosed no financial relationships with industry.

Reviewed by Zalman S. Agus, MD Emeritus Professor, Perelman School of Medicine at the University of Pennsylvania and Dorothy Caputo, MA, BSN, RN, Nurse Planner

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